These days, light olefins, in particular, light olefins such as ethylene or propylene, have been widely used in petrochemical industries. Generally, such light olefins have been mainly produced through steam cracking for thermally cracking (e.g., steam cracking) naphtha or kerosene in the presence of steam. Further, light olefin compounds have been limitedly produced as a by-product of FCC (Fluid Catalytic Cracking) mainly for use in the production of gasoline.
The steam cracking technique is typically conducted in a manner such that naphtha or kerosene is allowed to react at a high temperature of 800˜900° C. for a short residence time in the presence of steam. According to the steam cracking technique, the resultant olefins are of various types and have compositions that are determined within the limited range. In the steam cracking technique, various attempts have been made to correspond to cracking reaction conditions, such as high temperatures and short residence times, and to optimize energy efficiency. However, it is not easy to control the composition of olefins using the present steam cracking technique, and as well, the reaction takes place at 800˜900° C. and thus a lot of heat energy is required. Hence, there is a need for continuous advancement of the steam cracking technique.
In addition, light olefin compounds may be produced through FCC. Such an FCC process is a catalytic cracking technique using a catalyst in the form of fine particles which behave like fluid when being aerated using steam. Such a catalytic cracking technique is widely known in the art. Especially, in order to increase the yield of olefin (e.g., propylene) instead of gasoline, DCC (Deep Catalytic Cracking) is known as a modification of the FCC process. In the FCC process, a vacuum residue, an atmospheric residue, or gas oil has been used as the feedstock. However, FCC suffers because olefins are produced as the by-product.
The representative product yields of the above-mentioned processes are shown in Table 1 below.
TABLE 1Yield through Steam CrackingYield through FCCMethane16.131.2Ethylene32.051.9Ethane2.910.7Propylene16.654.8Propane0.350.7C410.949.1C55.711.1C6 or more14.1879.6Others1.080.9
In regard to the production of light olefins, there has been proposed an olefin production process through catalytic cracking, in addition to steam cracking and FCC. Particularly useful is a fluidized bed catalytic cracking process in the presence of a solid acid catalyst containing a large amount of HZSM-5 zeolite. Such olefin production processes through catalytic cracking have been developed to realize high production yields of light olefins using various hydrocarbons as the feedstock. In particular, these processes are characterized by high propylene yields, operation at lower temperatures than steam cracking, and easy recirculation of by-products.
More specifically, the related techniques are as follows.
U.S. Pat. No. 4,065,379 discloses a method of producing light olefins at high yields through FCC using a petroleum distillate, such as a vacuum residue, an atmospheric residue, or gas oil, as a feedstock, which requires a very high reaction temperature and results in an ethylene yield higher than a propylene yield.
U.S. Pat. No. 5,043,522 discloses a method of producing light olefins using a feedstock including 40˜95 wt % paraffins and 5˜60 wt % olefins through a fluidized bed catalytic cracking process, leading to 50 wt % or less reaction conversion rates.
U.S. Pat. No. 5,770,043 discloses a method of increasing the yield of light olefins using two risers, using a petroleum distillate such as gas oil as a feedstock, and re-circulating naphtha produced as an intermediate.
U.S. Pat. No. 6,307,117 discloses a method of separating a catalytic cracked product into H2˜C3 distillates and C4+ distillates. Further, a method of separation of the C4+ distillates into C4, C5˜C8 distillates, and C9+ distillates is disclosed. Still further, a method of additionally converting the C4+ distillates using a steam cracking reactor is introduced. However, these methods do not provide operation conditions for efficient use of the reaction product, in consideration of the properties of the catalytic cracking reaction.
U.S. Pat. No. 6,342,153 discloses a method of preparing a catalyst for use in the realization of high light olefin yields through an FCC process in a dilute pneumatic conveying regime using a petroleum distillate such as a vacuum residue, an atmospheric residue or gas oil as a feedstock.
U.S. Pat. No. 6,395,949 discloses a fluidized bed catalytic cracking process for enhancing the production of light olefins and aromatic compounds using a hydrocarbon feedstock and additionally introducing iso-pentane.
U.S. Pat. No. 6,602,920 discloses a process scheme for sequentially using a thermal cracking process, a hydrogenation process, and a catalytic cracking process to produce light olefins using natural gas as a feedstock. However, the process disclosed in this patent cannot be applied to the catalytic cracking process of the present invention using a hydrocarbon feedstock, preferably naphtha or kerosene.
U.S. Pat. No. 6,791,002 schematically discloses a method of connecting a plurality of risers in series or in parallel to increase the production of light olefins and a method for multiple feed streams, but specific reaction conditions and reaction results are not mentioned therein.
U.S. Pat. No. 6,867,341 discloses a catalyst for use in cracking of naphtha by controlling the distribution and crystal size of aluminum present in zeolite and a process therefor. According to this patent, aluminum present outside the pores is chemically neutralized to minimize the production of aromatic compounds on the surfaces of pores, whereas an acid site density is increased inside the pores using a catalyst having a high aluminum ion concentration, thus selectively increasing the production of ethylene and propylene having small sizes. However, only the general operation conditions including temperature and pressure of the catalytic cracking process are mentioned.
In this way, catalytic cracking processes for the production of light olefin hydrocarbons using various hydrocarbons as the feedstock have been actively developed. However, the additional development of processes for selectively producing light olefins, such as ethylene and propylene, from hydrocarbons that have high economic availability and may be used in great quantities as the feedstock, in particular, naphtha or kerosene, at high conversion rates and high selectivity is still urgently required.
In the process for producing light olefin hydrocarbons from hydrocarbon feedstock, preferably naphtha or kerosene, through catalytic cracking, in order to selectively produce light olefins such as ethylene and propylene at high conversion rates and high selectivity, the operation conditions of a riser, in which the catalytic cracking process is mainly conducted, are regarded as important. Especially, the fluidization and reaction in the riser may be more easily understood in consideration of the following theory.
As shown in FIG. 1, when a gas is supplied into the lower portion of a container packed with a solid catalyst, particles are fluidized. At a minimum fluidization velocity or higher, the flow regime is specifically divided into five regimes, including a bubbling regime, a slugging regime, a turbulent regime, a fast fluidization regime, and a dilute pneumatic conveying regime, respectively having different particle mobilities. Thus, in the case of a process using a fluidized bed reactor, a flow regime suitable for each process property should be set.
FIG. 2 shows the volume fraction of the catalyst in the reactor varying depending on the riser height, that is, on the flow regime. As shown in this drawing, it is confirmed that the total amount of the catalyst substantially present in the reactor considerably depends on the change in the flow regime. However, in the reaction involving the use of the catalyst, such as the fluidized bed catalytic cracking process, the total amount of the catalyst positively affects the performance of the process. Hence, the setting of the flow regime through the change in process operation conditions has a great influence on the reaction result.
Moreover, with the intention of determining the flow regime of the riser in the fluidization catalytic cracking process, many variables affecting the catalytic cracking reaction must be considered. As such, such variables include reaction temperatures, endothermic requirements, reaction times, catalyst sizes, catalyst circulation velocities, feedstock and catalyst ratios, inactivation of the catalyst due to the production of coke, strength of the catalyst, etc.
In particular, since the catalytic cracking of the hydrocarbon compound is an endothermic reaction, a lot of heat is required. Thus, in the case of the fluidized bed catalytic cracking process, desired reaction heat may be supplied through the circulation of hot catalyst, which is referred to as a circulating fluidization process. Accordingly, the riser of the circulating fluidization process for catalytic cracking of the hydrocarbon compound is operated in the fast fluidization regime or dilute pneumatic conveying regime, thereby maintaining efficient circulation of the catalyst.
As the typically commercialized catalytic cracking process of the hydrocarbon compound, there is FCC (Fluid Catalytic Cracking) for production of gasoline from petroleum distillate. Presently, the flow regime of the commercialized FCC is mainly operated in the dilute pneumatic conveying regime.
Specific techniques concerning the flow regime are as follows.
U.S. Pat. No. 4,548,138 discloses a combustor used in a fast fluidization regime, and the operation principle and mechanical device thereof are also mentioned.
U.S. Pat. No. 5,012,026 discloses a fluidized bed catalytic cracking process for converting paraffin hydrocarbons into light olefin, in which a turbulent regime is adopted as the main operation condition of the riser. In addition, a heat exchanger is used to supply heat required for an endothermic reaction, and the circulation and regeneration of the catalyst are minimized. However, there is no specific content related to a technique for realizing a high catalyst circulation rate necessary for the catalytic cracking process in the turbulent regime.
Therefore, in the process of producing light olefin hydrocarbons from the hydrocarbon feedstock, preferably naphtha or kerosene, using a fluidized bed catalytic cracking process, the operation conditions of the riser for the reaction, in particular, more efficient flow regime and process conditions thereof, are required.